The amount of information to be processed in electronic devices has been increased year by year. Along with the increase of the amount of information, optical transmission has been used in information transmission (signal transmission) at a short distance inside electronic devices. The reason for using optical interconnections (optical fibers) used in the optical transmission are that they are thinner, easier to bend, and more tolerant to noise than metal wires used in electric transmission. In addition, optical transmission has such an advantage that power consumption is less than that of electric transmission, particularly in high-speed transmission.
In such optical transmission, an optical transmission module for converting electric signals to optical signals or converting optical signals to electric signals is used. That is, an optical transmission module with a photoelectric conversion function is used in the optical transmission. More specifically, a communication chip and an optical transmission module are mounted on a substrate included in an electronic device. Such an optical transmission module converts electric signals inputted from the communication chip to optical signals or converts optical signals inputted externally to electric signals (Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2006-23777).
Under these circumstances, the optical transmission module used in the optical transmission is required to further reduce a mounting space or the cost.